Golf club

ABSTRACT

A golf club with an improved durability which realizes so thin a club head that the head can be enlarged, suppressing the increase of the total weight. A cold rolled material which is a beta type titanium alloy in a beta single phase and subjected to direct aging is used for the head. Preferably, the material is subjected to at least 15% cold rolling reduction. The aging is able to improve durability and surface hardness. Due to the direct aging of the cold worked material without solution treatment, such a long time heat treatment is no longer necessary, thereby resulting in the reduction of production costs.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application is a continuation-in-part application of U.S.Appl. Ser. No. 09/454,426 filed on Dec. 3, 1999, and now pending.

BACKGROUND OF INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a golf club, particularly to thematerial of a club head.

[0004] 2. Description of the Prior Art

[0005] In a golf club head, one of means for enlarging the sweet area,i.e., an area on a face where a ball travels comparatively straight andwell when struck thereon, is to large-size a club head itself. In recentyears, some heads with more than 300 cc volume have come onto themarket. Even if a club head is large-sized, yet the total weight thereofmust be suppressed so as to ensure the easiness to handle. As a result,the head must be formed hollow inside, and its outer shells must bethinned. However, thinned outer shells generally lead to decreasedstrength of a club head, even to the likelihood of the head beingdamaged due for example to the impact force at the time of strikingballs. As you need ensure sufficient strength of a face for strikingballs, a face has heretofore been formed to at least 3.0 mm thickness.

[0006] The main current of recent golf clubs has been directed totitanium or titanium alloy head. As titanium alloy is lighter butstronger than stainless steel, the degree of freedom in designing a headis increased, thereby generally enabling the manufacture of a club headwhich is larger than a head made of stainless steel. Consequently, thesweet area is enlarged, as mentioned above, so that the stable flight ofgolf balls can be obtained.

[0007] Conventional titanium alloy based materials for a golf club headhave been alpha+beta type alloys such as Ti-6Al-4V alloys andTi-4.5Al-3V-2Fe-2Mo alloys, or beta type alloys such asTi-15V-3Cr-3Sn-3Al alloys, and etc.. The Ti-6Al-4V alloys have been mostfrequently used among such titanium alloys in various industrial fields,which however, are not suitable for cold working, and thus a great dealof labor and costs have been required to form a plate to a 1 to 5 mmthickness, the dimension generally required for the materials of a golfclub. Therefore, casting has been employed for manufacturing suchTi-6Al-4V alloy made head, as disclosed in Japanese Patent Un-ExaminedPublication No.3-230845. However, as titanium is an easily oxidizablemetal, casing is not able to be carried out in the atmosphere. Further,titanium is easily reacted with a casting mold, and thus extremely hightechnology is required, thereby eventually leading to increased costs.In addition to the foregoing, castings have a drawback of resultantinferior strength, because they can not undergo tissue-control ascompared to rolled materials. In contrast, ultra plasticity working ispossible for the aforesaid Ti-4.5Al-3V-2Fe-2Mo alloys, and thus highstrength is more easily obtained by the alloys than by castings.However, as even the plasticity working requires special installations,and is highly time-consuming, the method is not suitable for massproduction. Under the above-mentioned circumstances, beta type alloyswith better working ability, such as Ti-15Mo-5Zr-3Al andTi-15V-3Cr-3Sn-3Al, have more often come to be used. These alloys areformed by cold working to a preset thickness, and then are subjected tothermal treatment for removing distortions caused by cold working andundergoing solution treatment, thereby assembling them into a golf clubhead.

[0008] For related prior art, Japanese Un-Examined Patent PublicationNo.9-59731 discloses a titanium alloy for golf club head, said titaniumalloy containing: zirconium and oxygen by the amounts in the rangessatisfying the following inequalities: the weight percentage content ofZr≧1.0(%), in which Zr+25O₂≧5(%), and 3 X Zr+220 X O₂≦86(%); a slightamount of at least one selected from among aluminum, tin, copper, andchromium; and titanium and inevitable impurities as the remainingcomponents. This prior art also teaches the manufacture of a face of agolf club head by subjecting such titanium alloy to final rolling toeffect 30% or more reduction in area, at 700° C. or below. In the priorart, such titanium alloy is referred to as alpha type titanium alloy. Infact, Zr is not a beta stabilized element. Further, the prior artpublication refers to the difficulty in cold working in a case where abeta stabilized element is added. Accordingly, the art disclosed by thisprior art publication is not intended for beta type titanium alloy.

[0009] On the other hand, Japanese Un-Examined Patent Publication No.11-19255 describes that the face member and head body member of a golfclub head are each formed from beta-type titanium alloy. The prior artpublication discloses a method for manufacturing a golf club head suchthat the face member is subjected to cold or hot forging to becomeplastically deformed to have a predetermined configuration. This priorart publication also describes that the face member can have a thicknessof about 2.7 mm at the central portion thereof. Although this prior artteaches the use of cold or hot forging as a method of working the facemember of a golf club head, it is silent with any advantage such as theimprovement of durability to be resulted therefrom, only describing thatany suitable methods may be selectively used for forging, irrespectiveof either cold or hot forging, and thus, it only refers to the types offorging as examples. In fact, cold working is generally subjected to alarge deformation resistance, resulting in inferior workability, so thatit is difficult to carry out. Accordingly, it is unlikely for thoseskilled in the art to select cold working. Further, even though thetechniques disclosed by the prior art is used to cold work a beta typetitanium alloy, yet it is not possible to manufacture a good club head.In other words, whilst a titanium alloy has extremely high specifictensile strength (strength/density) and corrosion resistance amongpractical metallic materials, and thus it has higher specific tensilestrength and corrosion resistance than steel materials such as S45C, yetit has a drawback that due to its poor cold working ability, the coldworking of a beta type titanium alloy is not a suitable method formanufacturing a face of a golf club head.

[0010] Whereas, Japanese Un-Examined Patent Publication No.9-215786discloses that the face member of a golf club head is formed from a betatype titanium alloy. Specifically, this prior art publication disclosesthat when manufacturing the face member, a shoulder round bar is heatedup to a temperature range for hot working and then die-forged to obtaina desired shape thereof, which is then subjected to direct agingtreatment without solution treatment, to thereby form the face memberhaving desired properties including desired strength. This prior artfurther describes that as the solution treatment is omitted after thehot die-forging, the production process is simplified, and the strengthis enhanced due to the synergy of work hardening and age hardening.However, even if the material is subjected to direct aging treatmentafter the hot die-forging process, the strength thereof is still toosmall for the material to be used for that of the face member that isrequired to have the smallest possible thickness, and thus it isinevitably cracked due to the impact at the time of striking balls.

[0011] Also, Japanese Un-Examined Patent Publication No. 10-71219discloses a forging step in which a titanium-made material bar is heatedto hot forging temperature and die-forged to form the face member, andan aging treatment step for subjecting the same to aging treatmentwithout solution treatment after the forging step. However, if thedirect aging treatment is performed after the hot die-forging step, yetthe same problem as mentioned in the foregoing paragraph occurs for thesame reasons.

[0012] Also, Japanese Un-Examined Patent Publication No. 5-70909discloses a method of manufacturing an aluminum alloy pipe for use withhydraulic machines, in which an aluminum alloy ingot is hot extruded,drawn, and then subjected to aging treatment. Specifically, this priorart discloses that the reduction in cross sectional area after thedrawing process should be 15 to 25%, relative to the cross sectionalarea after the hot extrusion process. This prior art publication teachesthat the reason why the 15-25% reduction in cross sectional area by thedrawing process, which, in other words, is 15-25% cold work reduction,is preferred is that in the case of the reduction of 15% or below, theintroduction of cold strain is too little to obtain sufficient strengtheven through the aging treatment, while in the case of the reduction of25% or above, lowered ductility is resulted thereby leading to loweredformability in bending process or pipe-enlarging process. However, itshould be noted that the prior art includes no teachings nor suggestionsconcerning the manufacture of a golf club. Further, it is true that coldreduction is referred to therein, but a beta type titanium alloy hassuch a poor cold working ability in general that it is not suitable forthe manufacture of the face member of a golf club head.

[0013] Also, in Japanese Un-Examined Patent Publication No. 62-151551 isdisclosed a method of manufacturing a Ti-15V-3Cr-3Sn-3Al titanium alloyfor use as a cold worked material, in which the alloy is subjected tosolution heat treatment by retaining it at 830 to 1150° C. for 3 minutesto 5 hours and then cooling it at more than 18° C./minute cooling rate,which is then cold worked to more than 50% cold reduction.

[0014] Specifically, this prior art publication teaches that theadvantage of more than 50% cold rolling rate is in that with more than50% rate, the crystal particle size of the re-crystallized material thatwas subjected to high temperature preliminary solution treatment, coldrolling and then solution treatment becomes smaller than that of thematerial that was subjected to low temperature preliminary solutiontreatment, cold rolling, and then solution treatment. The prior art alsomentions solution aging treatment, and describes that the titanium ortitanium alloy thus obtained is suitable as a material for a rocketship, various kinds of chemical plants, desalination plant and the like,but it does not include any descriptions relating to golf club head.Further, cold working reduction is referred to therein, but a beta typetitanium alloy generally has such a poor cold working ability that it isnot suitable for the manufacture of the face member of a golf club head.

[0015] In recent years, however, a face has been required to be thinnedstill further in order to make a ball travel a still longer distance,which has caused a problem such that beta type alloy materials of golfclub head which are manufactured by the above-mentioned conventionalprocesses are not strong enough to prevent the cracks from developingdue to the impact force at the time of striking balls. The cracks arepresumably due to a face being too much thinned to a thickness of lessthan 3 mm when only a face of 3 mm or above could withstand the impact.

SUMMARY OF THE INVENTION

[0016] To eliminate the above-mentioned problems, it is, therefore, aprimary object of the present invention to provide a golf club withexcellent durability.

[0017] To attain the above object, there is proposed, from a firstaspect of the invention, a golf club with a certain metallic materialused for the face member of a golf club head, said metallic materialbeing cold rolled so as to indicate 15% or more cold rolling reduction.Specifically, as cold rolling is employed as cold working, the formingof a beta type titanium alloy to a thin thickness by cold rolling leadsdirectly to the forming of the face member close to a preset thinthickness. Thus, if a beta type titanium alloy generally has a poor coldworking ability, yet it is possible to easily form the face member to apreset thin thickness, such as 3 mm or below, by cold rolling the same.Further, due to the cold rolling, deformation speed can be lowered,thereby making cracks less likely to occur. Furthermore, with suchenhanced cold rolling reduction of 15% or above, the work-hardeningcaused by the cold working is allowed to remain, thus improving thedurability and surface hardness of the material.

[0018] From a second aspect of the invention, there is also proposed agolf club with a certain metallic material used for a golf club head,said metallic material being a cold rolled material which is thensubjected to direct aging. With such aging, the durability and surfacehardness of the material can be improved. Further, by subjecting thecold rolled material to direct aging without solution heat treatment,there is no longer need of such a long heat treatment time to obtain asufficient hardness, due to work hardening by cold rolling as well asaging precipitation that proceeds more rapidly, whereby manufacturingcosts can be suppressed.

[0019] From a further aspect of the invention, there is proposed a golfclub with a certain metallic material used for a golf club head, saidmetallic material being subjected to direct aging treatment attemperature ranging from 300 to 600°3. Thus, the cold rolled materialcan be effectively hardened, without removing strains and without beingre-crystallized.

[0020] From a still further aspect of the invention, there is proposed agolf club with a certain metallic material used for a golf club head,said metallic material being a cold rolled material of beta typetitanium alloy in a single beta phase that is subjected to direct aging.Due to the aging, the durability and surface hardness of the material isimproved. Further, by subjecting the cold rolled material to directaging without solution heat treatment, a long-time heat treatment is nolonger necessary to obtain sufficient hardness, whereby manufacturingcosts can be suppressed.

[0021] Specifically, whilst a beta type alloy is an alloy of so-calledprecipitation hardening type to allow the precipitation of an alphaphase in a beta phase by aging treatment to thereby obtain hardness, thedirect aging treatment without releasing distortions or strains causedby working a head structuring member through cold rolling and pressing,can facilitate the precipitation of an alpha phase, without removing theeffect of work hardening generated by cold working so as to leave thesame effect at such a low temperature needed for aging, whereby a highstrength can be obtained in a short time. Furthermore, as such betasingle phase has neither a two-layer tissue nor a fragile tissue, nocracks will be developed at the time of cold or hot press working.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Other objects, features and advantages of the invention will beapparent to those skilled in the art from the following description ofthe preferred embodiments of the invention, wherein reference is made tothe accompanying drawings, of which:

[0023]FIG. 1 is a perspective view showing a golf club of an embodimentof the invention;

[0024]FIG. 2 is a section of a golf club of FIG. 1;

[0025]FIG. 3(A) is a section of a golf club of FIG. 1, taken alongIII-III line thereof, particularly illustrating a state without cracks;and

[0026]FIG. 3(B) is a section of a golf club of FIG. 1, taken alongIII-III line thereof, particularly illustrating a state with cracks.

DETAILED DESCRIPTION OF THE INVENTION

[0027] Hereinafter is explained an embodiment of a golf club of theinvention with reference to the attached drawings.

[0028]FIGS. 1 and 2 illustrate one example of a golf club in accordancewith the invention. The golf club is a wood club, or a so-called metalwood with a metallic, hollow head 1. The head 1 comprises a face 2 forstriking balls on a front face, a back 3 at a rear side, a sole 4 at alower part, a crown 5 at a top part, a toe 6 at one side and a heel 7 atthe other side, respectively. An upper part of the heel 7 is formed witha neck 8, from which extends a hosel 9 upwardly. The hosel 9 serves as ashaft connector for connecting a shaft 10 thereto. The head 1 has ahollow interior 11, which may be filled with suitable filler such aspolyurethane. Further, the face 2 is formed with a plurality of groovescalled score lines 12.

[0029] The head 1 is constructed of three shells, namely, a tabular facemember 16, a body member 17 and a crown member 18 which construct theouter shell of the head 1. The face member 16 constructs the face 2,while the crown member 18 constructs the crown 5, and the body member 17the remaining portions such as the back 3 and the sole 4. These facemember 16, body member 17 and crown member 18 are joined together bymeans of welding or the like. In the meantime, the head 1 may be dividedin a different manner than the above-mentioned, into for example twopieces with one piece making up of the face 2 side while the other theback 3 side, or into four or more pieces.

[0030] In the event that the head 1 made of conventional materials isthinned, cracks are liable to occur due to impact at the time ofstriking balls. After investigating the cracks thus caused, a findingfollowed that splits did not occur in portions which were consideredshort of strength, such as welded parts, but in bottom portions of scorelines so that the splits developed therein spread all over the face 2 tothereby cause cracks. FIG. 3 illustrates score line 12 as well as howits crack 21 occurred. A further finding followed that such tendencytoward cracks are observed mainly on the bottom portions of the scorelines 12 located in the center of the face 2. Analyzing such phenomenonfrom a material strength's point of view revealed that the load of morethan 1 ton or above was applied to the face 2 at the time of striking aball, and thus the entire face 2 was bent toward the inside of the head1 due to the shortage of strength, so that a stress thus developed wasconcentrated upon the bottom portions of the score lines 21, whichresulted in the facilitating and developing of the cracks. To preventsuch phenomenon, it was found out that the improvement of the durabilityand surface hardness of a material is necessary from an aspect ofmaterial. It should be noted that improved durability can compensate forthe shortage of strength of the thinned face 2, preventing the same frombeing bent toward the inside of the head 1 at the time of strikingballs. Also, improved surface hardiness can prevent the localdeformation of a ball striking portion, dispersing the aforesaid stressconcentrated upon the bottom portions of the score lines 12 towardperipheral portions. Furthermore, the durability of the materialproperly improved to the extent that it does not become fragile cancontribute, fortunately, to the improvement of fatigue characteristicsof the material itself, having an effect on the prevention of cracks 21.

[0031] To reflect the aforesaid material analysis result to materialcharacteristics, various experiments were repeatedly performed, whichwere followed by a finding that to attain the aforesaid object throughthe effective use of conventional manufacturing apparatus, the face 2must be subjected to an optimal aging treatment thereby to obtaindurability and surface hardness sufficient enough to prevent the cracksfrom developing. As a result, optimal material characteristics have beengrasped. On the other hand, the aging condition for obtaining higherdurability than in the past, requires extremely long heat treatmenttime, which brought about another problem of production costs beingdrastically increased.

[0032] Through the study and review to solve this new problem, it wasfound out that the problem could be solved by subjecting a golf clubproduct which was worked up to a stage of determining a productthickness to direct aging without solution treatment. Based on thisfinding, there could be obtained a golf club head made of titanium alloywhich has excellent durability. That is, a golf club of the inventionemploys a cold rolled material, particularly a cold rolled beta typetitanium alloy in a beta single phase that was subjected to direct agingtreatment, for the material of the head constructing members 16, 17 and18, particularly for that of the face 16. In a preferred form of theinvention, the employed material should indicate at least 15% coldrolling reduction.

[0033] As above discussed, a beta type titanium alloy has heretoforebeen used for a material of the face member of a golf club, with theaged tissues from the re-crystallization state. According to the priorart, however, long hours of aging treatment at comparatively hightemperature (at 500° C. for eight hours, for example) must be performed(full aging), in order to obtain comparatively even tissues andsubstantial strength. Although it is possible to obtain more even agedtissues through the aging treatment at 400 to 450° C. for dozens ofhours, hardness becomes too high when such even tissues have beenobtained, and thus the material would have inferior ductility,particularly indicate poor tenacity in the case that cutouts are presentin the product.

[0034] Further, irrespective of whether it is cold aging or hot aging,the priority precipitation of alpha phase into grain boundary isinevitable, and thus sufficient toughness to compensate for the thinnedthickness cannot be obtained, so that durability is impaired.

[0035] In contrast, if alpha phase is allowed to precipitate fromtissues which are not re-crystallized yet, the priority precipitation ofalpha phase into the grain boundary is suppressed, so that the alphaphase is allowed to precipitate speedily in the grain and the grainboundary to substantially the same extent, thus facilitating theprecipitation of alpha phase substantially over an entire region. As aresult, if aging is not fully performed to reach a fully aged state, yeteven tissues can be obtained, and if the alpha phase is not fullyprecipitated, yet the material can obtain certain strength, thusmaintaining high ductility as well as high tenacity. Whilst theforegoing advantageous effects can be realized through cold rolling ofseveral percentages' cold reduction, such as so-called skin passrolling, the durability of the material can be enhanced noticeablypreferably at 15% or more cold rolling reduction. Further, with the betagrain being kept fine enough in the beta phase, better ductility can beobtained, as is well known.

[0036] The reason why the titanium alloy tissue prior to aging is in abeta single phase in the present invention, is that the presence offragile tissues such as alpha+beta two-phase tissue or omega tissuecould develop cracks when cold or hot pressing the head constructingmembers. Further, the reason why the material prior to aging step has tohave the cold rolled tissues in the invention is to obtain sufficientstrength when aging the head 1 at the final stage. Tissues subjected tosolution heat treatment are, unlike the cold rolled tissues, not able torealize sufficient strength through a short-time aging, thus leading toa likelihood of developing cracks or the like due to impact at the timeof striking balls. Further, at least 15% cold rolling ratio can fullyrealize this advantageous effect. In addition, the direct agingtreatment without solution heat treatment in the heat treatment of thehead 1 is aimed at obtaining higher strength by subjecting the head 1 todirect aging.

[0037] As above mentioned, the head 1 is formed from the material havingcold rolled tissues, said material being subjected to aging withoutsolution heat treatment, thereby obtaining high strength.

[0038] Whilst a beta type alloy is an alloy of so-called precipitationhardening type to allow the precipitation of an alpha phase in a betaphase by aging treatment to thereby obtain hardness, the direct agingtreatment without allowing solution heat treatment to releasedistortions developed by working the head structuring members throughcold rolling and pressing, can facilitate the precipitation of an alphaphase, and leave the work hardening effect generated by the cold rollingstep even at such a low temperature needed only for aging, withoutremoving such effect, as compared to the aging treatment of the materialafter the solution heat treatment. Through the foregoing twoadvantageous effects, a higher strength can be obtained in a short time.

[0039] Although high strength can be realized by using materialsmanufactured according to conventional methods, yet it would require along-time aging treatment, so that some disadvantages would occur suchas the increase of manufacturing costs and the decrease of productivity.Thus, they are unlikely to provide realistic solution to theabove-mentioned problems.

[0040] A preferred method for manufacturing a golf club of the inventioncomprises the steps of: producing an ingot from an alloy material ofrequired composition by means of arc welding; forming the ingot intoplate materials of a preset thickness by means of hot and cold rolling;fabricating members of respectively preset shapes (i.e., said facemember 16, body member 17 and crown member 18) by means of hot or coldpressing and then assembling these members into the head 1 by joiningthem together by welding; subjecting the head 1 thus obtained to agingtreatment; and assembling a golf club by connecting the shaft 10 to thehead 1.

[0041] It should be noted, however, that a particular attention must bepaid to the hot rolling step in order to effectively work the invention.

[0042] In the event that any other phase than the beta phaseprecipitates due to the hot rolling, a solution heat treatment isnecessary thereafter, in order for the subsequent cold working step tobe performed with no problems. However, temperature control, ifpossible, to finish to the beta single phase only during the hotrolling, would enable the manufacturing at low costs. In addition tothat, by developing distortions during the hot rolling step, sufficientwork hardening can be obtained, even though the subsequent cold workingis not carried out sufficiently, thereby realizing low-costmanufacturing.

[0043] Another attention needs to be paid to the cold working as well.With conventional methods where solution heat treatment is performedafter the final working, configurations could be corrected by heatingduring the treatment. In a preferred form of the invention where nosolution heat treatment is performed after the cold working, suchcorrection is not carried out and thus full configurations must bepreformed by the cold working step.

[0044] Also, a further attention needs to be paid to the problem of theabsorption of hydrogen. The beta type titanium alloy is liable to absorbhydrogen, and thus if the absorption of hydrogen has taken place, itmust undergo high temperature heat treatment in either vacuum or Arambient atmosphere. Although dehydrogenation was possible through thesolution heat treatment in the conventional methods, which would beaccompanied by difficulties, a particular attention must be paid not toabsorb hydrogen during the steps in the invention. Specifically, as acidcleaning is a step which is liable to cause the absorption of hydrogen,acid cleaning liquid such as solution of hydrofluoric acid and nitricacid, temperature and time for acid cleaning must be carefullycontrolled. TABLE 1 Aging Hardness: Durabilty Working ConditionCondition HV1.0 (N/mm²) Remarks solution treatment 450° C./ 341  997 1stcomparative 8 hours example solution treatment 450° C./ 357 1038 1st +10% cold working 8 hours embodiment solution treatment 450° C./ 393 11792nd + 15% cold working 8 hours embodiment solution treatment 450° C./415 1244 3rd + 30% cold working 8 hours embodiment solution treatment450° C./ 450 1387 4th + 50% cold working 8 hours embodiment hotrolling + direct 450° C./ 427 1262 5th 30% cold working 8 hoursembodiment

[0045] The above table 1 shows the result of measurement of post-aginghardness and durability concerning the respective materials. Moreprecisely, a beta type alloy or Ti-15V-3Cr-3SN-3Al alloy was hot rolledand then solution treated, which was either cold rolled or not coldrolled, and then subjected to aging treatment for investigating thechanges of hardness. The condition for aging treatment was 450° C. for 8hours for all the samples.

[0046] As is clearly seen from the table 1, whilst the hardness of amaterial that was hot rolled and then solution treated was not more than341 even through the aging for 8 hours at 450° C., the hardness of thematerial which was further through the cold rolling was increased afterthe aging under the same condition. This is due to the work hardeningeffect caused by the cold rolling and the aging precipitation havingproceeded more rapidly. Specifically, when cold rolling ratio was 15% orabove, these effects appeared more noticeably. Further, it turned outthat when the hot rolled material was direct cold rolled, and thensubjected to aging treatment without solution heat treatment, thehardness became still higher. Although the embodiments are under thesame aging condition at 450° C., the same effects were acknowledged ofunder lower temperature conditions such as at 400° C. or at 300° C.Although the similar effects could be obtained even in a range higherthan 450° C., the age hardening will not proceed at 600° C. or above,and distortions will be removed or the re-crystallization will occur insuch higher temperature range, so that the effects are likely to bedecreased. In other words, the aging temperature is preferably in arange of from 300° C. to 600° C. TABLE 2 The number of trial Type ofThick- Type of Heat strikes to face member ness(mm) treatment causecracks Remarks 30% cold rolled 2.7 aging no cracks 6th even afterembodiment 5,000 or more trials 50% cold rolled 2.7 aging no cracks 7theven after embodiment 5,000 or more trials 30% cold rolled 2.7 solution3200 2nd treatment + comparative aging example 0% cold rolled 2.7solution 2500 3rd treatment comparative example hot rolled 2.7 solution2700 4th treatment + comparative aging example hot rolled 2.7 Solution1000 5th treatment comparative example

[0047] The above table 2 shows the data on the durability of the head 1made from Ti-15V-3Cr-3Sn-3Al alloy of the invention. The data were takenusing a swing robot for golf.

[0048] As is apparent from the above, for golf clubs with the face madeof materials subjected to the solution treatment only or the solutiontreatment and the subsequent aging treatment, cracks or depressionsappeared on the face 2 during trial striking, indicating inferiorresults. For the embodiments of the invention where the material wascold rolled and then subjected to the aging treatment, no cracks anddepressions were found even after trial striking of 5,000 times,indicating superior results.

[0049] With the thickness t1 of the face 2 being 2.7 mm which is smallerthan any conventional titanium-made faces of golf clubs, the number oftrial strikes to cause cracks apparently differed between the facemembers 16 of the invention and those not according to the invention.The result well demonstrates that the present invention is particularlyadvantageous as a golfing driver. TABLE 3 Thickness Preset head The HeadBall Travelling of face speed number of speed speed distance(yard) No.(mm) (m/s) trials (m/s) (m/s) carry run total (1) 3.0 40 1 40.1 53.7 17720 197 2 40.2 54.0 177 28 205 3 40.0 54.1 178 26 204 4 40.2 53.8 179 20199 5 39.9 54.1 181 22 203 Average 40.1 53.9 178 23 202 (2) 2.7 40 140.7 54.8 186 21 207 2 40.7 54.8 186 21 207 3 40.9 55.0 184 23 207 440.7 54.9 185 22 207 5 40.9 54.9 185 24 209 Average 40.8 54.9 185 22 207

[0050] Table 3 shows the result of performance test of a golf club headaccording to the embodiment, in which a swing robot for striking a golfball was used to test a golfing driver. In the table 3, (1) indicates adriver of prior art, while (2) a driver according to the embodiment. Inother words, (2) was a driver whose constructing members including aface member are made from a beta type titanium alloy in a beta singlephase which are cold rolled up to 15% reduction or above and thensubjected to direct aging treatment, while (1) was the one in which suchbeta type titanium alloy was subjected to solution treatment and then toaging treatment.

[0051] The head of (2) has a face member of 2.7 mm thickness, with ahead volume of 300 cm³, while the head of (1) has a face member of 3.0mm thickness, with a head volume of 250 cm³, both heads defining thesame loft angle of 10.5 degrees.

[0052] For both heads, head speed was set at 40 m/s, which were notchanged throughout the trials, and right-striking angle was approximatedto zero to minimize the deviation in the sidewise direction. In thetable, numerical values in the column for indicating the head speed arethe actual ones obtained by measurement, In the column for travelingdistance, “carry” means a distance that a ball traveled in the air,“run” means a distance that a ball traveled on the ground, and “total”means the sum thereof, respectively.

[0053] As is apparent from the table 3, the driver (2) of the embodimentof the invention indicated higher initial ball speed. In other words,the average of ball speed was 54.9 m/s in the driver of (2), while itwas 53.9 m/s in the driver of (1) or conventional driver, and thus thespeed was improved by 1 m/s (1.8%). Further, the average of “carry” andthe average of “total” were 185 yards and 207 yards in the driver of(2), respectively, while they were 178 yards and 202 yards in the driverof (1), and thus the ball travelling distance were improved by 7 yards(4%) and 5 yards (2.5%), respectively.

[0054] The above result well demonstrates that according to conventionalmethod in which aging treatment is carried out after solution treatment,the face member must have at least 3.0 mm thickness to insure strength,and thus a golf club head cannot be large-sized, so that a greatrepulsive force against balls can not be expected. According to thetechnique of the invention, however, the face member are made from abeta type titanium alloy in a beta single phase which are cold rolled upto 15% reduction or above and then subjected to direct aging treatment,it is possible to form the face member as thin as 2.7 mm, thus enablingthe large-sizing of a head, so that the repulsive force against ballscan be enhanced without sacrificing strength thereof.

[0055] Incidentally, the present invention should not be limited to theforegoing embodiments, but may be variously modified within a scope ofthe invention. For example, the invention is also applicable to ironclubs, though the embodiments take a wood club as an example.

What is claimed:
 1. A golf club having a head, said head beingconstructed of a plurality of members including a face member, wherein acold rolled beta type titanium alloy which is subjected to direct agingtreatment is used for a material of the face member.
 2. A golf clubaccording to claim 2, wherein said aging treatment is performed in arange of from 300° C. to 600° C.
 3. A golf club according to claim 1,wherein said beta type titanium alloy is in a beta single phase.
 4. Agolf club according to claim 2, wherein said beta type titanium alloy isin a beta single phase.
 5. A golf club according to claim 3, whereinsaid material is hot rolled into a beta single phase, which is then coldrolled and subjected to direct aging treatment.
 6. A golf club accordingto claim 4, wherein said material is hot rolled into a beta singlephase, which is then cold rolled and subjected to direct agingtreatment.
 7. A golf club having a head, said head being constructed ofa plurality of members including a face member, wherein a beta typetitanium alloy which is cold rolled to 15% cold reduction is used for amaterial of the face member.
 8. A golf club according to claim 7,wherein said cold rolled material is subjected to direct agingtreatment.
 9. A golf club according to claim 8, wherein said agingtreatment is performed in a range of from 300° C. to 600° C.
 10. A golfclub according to claim 7, wherein said cold rolled material is a betatype titanium alloy in a beta single phase.
 11. A golf club according toclaim 8, wherein said cold rolled material is a beta type titanium alloyin a beta single phase.
 12. A golf club according to claim 9, whereinsaid cold rolled material is a beta type titanium alloy in a beta singlephase.